Unsupervised colour image segmentation by low-level perceptual grouping

This paper proposes a new unsupervised approach for colour image segmentation. A hierarchy of image partitions is created on the basis of a function that merges spatially connected regions according to primary perceptual criteria. Likewise, a global function that measures the goodness of each defined partition is used to choose the best low-level perceptual grouping in the hierarchy. Contributions also include a comparative study with five unsupervised colour image segmentation techniques. These techniques have been frequently used as a reference in other comparisons. The results obtained by each method have been systematically evaluated using four well-known unsupervised measures for judging the segmentation quality. Our methodology has globally shown the best performance, obtaining better results in three out of four of these segmentation quality measures. Experiments will also show that our proposal finds low-level perceptual solutions that are highly correlated with the ones provided by human

Item response theory in AI: Analysing machine learning classifiers at the instance level

[EN] AI systems are usually evaluated on a range of problem instances and compared to other AI systems that use different strategies. These instances are rarely independent. Machine learning, and supervised learning in particular, is a very good example of this. Given a machine learning model, its behaviour for a single instance cannot be understood in isolation but rather in relation to the rest of the data distribution or dataset. In a dual way, the results of one machine learning model for an instance can be analysed in comparison to other models. While this analysis is relative to a population or distribution of models, it can give much more insight than an isolated analysis. Item response theory (IRT) combines this duality between items and respondents to extract latent variables of the items (such as discrimination or difficulty) and the respondents (such as ability). IRT can be adapted to the analysis of machine learning experiments (and by extension to any other artificial intelligence experiments). In this paper, we see that IRT suits classification tasks perfectly, where instances correspond to items and classifiers correspond to respondents. We perform a series of experiments with a range of datasets and classification methods to fully understand what the IRT parameters such as discrimination, difficulty and guessing mean for classification instances (and their relation to instance hardness measures) and how the estimated classifier ability can be used to compare classifier performance in a different way through classifier characteristic curves.This work has been partially supported by the EU (FEDER) and the Ministerio de Economia y Competitividad (MINECO) in Spain grant TIN2015-69175-C4-1-R, the Air Force Office of Scientific Research under award number FA9550-17-1-0287, and the REFRAME project, granted by the European Coordinated Research on Long-term Challenges in Information and Communication Sciences Technologies ERA-Net (CHIST-ERA) and funded by Ministerio de Economia y Competitividad (MINECO) in Spain (PCIN-2013-037), and by Generalitat Valenciana PROMETEOII/2015/013. Fernando Martinez-Plumed was also supported by INCIBE (INCIBEI-2015-27345) "Ayudas para la excelencia de los equipos de investigacion avanzada en ciberseguridad", the European Commission (Joint Research Centre) HUMAINT project (Expert Contract CT-EX2018D335821-101), and Universitat Politecnica de Valencia (PAID-06-18 Ref. SP20180210). Ricardo Prudencio was financially supported by CNPq (Brazilian Agency). Jose Hernandez-Orallo was supported by a Salvador de Madariaga grant (PRX17/00467) from the Spanish MECD for a research stay at the Leverhulme Centre for the Future of Intelligence (CFI), Cambridge, a BEST grant (BEST/2017/045) from the Valencia GVA for another research stay also at the CFI, and an FLI grant RFP2.Martínez-Plumed, F.; Prudencio, R.; Martínez-Usó, A.; Hernández-Orallo, J. (2019). Item response theory in AI: Analysing machine learning classifiers at the instance level. Artificial Intelligence. 271:18-42. https://doi.org/10.1016/j.artint.2018.09.004S184227

Depth Estimation in Integral Imaging Based on a Maximum Voting Strategy

An approach that uses the scene information acquired by means of a three-dimensional (3D) synthetic aperture integral imaging system is presented. This method generates a depth map of the scene through a voting strategy. In particular, we consider the information given by each camera of the array for each pixel, and also the local information in the neighbourhood of that pixel. The proposed method obtains consistent results for any type of object surfaces as well as very sharp boundaries. In addition, we also contribute in this paper with a repository of a set of synthetic integral images generated by 3DS Max where the so-called ground truth (real-true depth map) is available. This resource can be used as a benchmark to test any Integral Imaging based range estimation method.This work was supported in part by the Spanish Ministry of Economy and Competitiveness (MINECO) under the projects SEOSAT (ESP2013-48458-C4-3-P) and MTM2013-48371-C2-2-P, in part by the Generalitat Valenciana through the project PROMETEO-II-2014-062, and in part by the University Jaume I through the project UJI-P11B2014-09. The work of B. Javidi was supported by the National Science Foundation under Grant NSF/IIS-1422179

Reframing in context: A systematic approach for model reuse in machine learning

We describe a systematic approach called reframing, defined as the process of preparing a machine learning model (e.g., a classifier) to perform well over a range of operating contexts. One way to achieve this is by constructing a versatile model, which is not fitted to a particular context, and thus enables model reuse. We formally characterise reframing in terms of a taxonomy of context changes that may be encountered and distinguish it from model retraining and revision. We then identify three main kinds of reframing: input reframing, output reframing and structural reframing. We proceed by reviewing areas and problems where some notion of reframing has already been developed and shown useful, if under different names: re-optimising, adapting, tuning, thresholding, etc. This exploration of the landscape of reframing allows us to identify opportunities where reframing might be possible and useful. Finally, we describe related approaches in terms of the problems they address or the kind of solutions they obtain. The paper closes with a re-interpretation of the model development and deployment process with the use of reframing.We thank the anonymous reviewers for their comments, which have helped to improve this paper significantly. This work was supported by the REFRAME project, granted by the European Coordinated Research on Long-term Challenges in Information and Communication Sciences Technologies ERA-Net (CHIST-ERA), funded by their respective national funding agencies in the UK (EPSRC, EP/K018728), France and Spain (MINECO, PCIN-2013-037). It has also been partially supported by the EU (FEDER) and Spanish MINECO grant TIN2015-69175-C4-1-R and by Generalitat Valenciana PROMETEOII/2015/013.Hernández Orallo, J.; Martínez Usó, A.; Prudencio, RBC.; Kull, M.; Flach, P.; Ahmed, CF.; Lachiche, N. (2016). Reframing in context: A systematic approach for model reuse in machine learning. AI Communications. 29(5):551-566. https://doi.org/10.3233/AIC-160705S55156629

Multidimensional Optical Sensing and Imaging Systems (MOSIS): From Macro to Micro Scales

Multidimensional optical imaging systems for information processing and visualization technologies have numerous applications in fields such as manufacturing, medical sciences, entertainment, robotics, surveillance, and defense. Among different three-dimensional (3-D) imaging methods, integral imaging is a promising multiperspective sensing and display technique. Compared with other 3-D imaging techniques, integral imaging can capture a scene using an incoherent light source and generate real 3-D images for observation without any special viewing devices. This review paper describes passive multidimensional imaging systems combined with different integral imaging configurations. One example is the integral-imaging-based multidimensional optical sensing and imaging systems (MOSIS), which can be used for 3-D visualization, seeing through obscurations, material inspection, and object recognition from microscales to long range imaging. This system utilizes many degrees of freedom such as time and space multiplexing, depth information, polarimetric, temporal, photon flux and multispectral information based on integral imaging to record and reconstruct the multidimensionally integrated scene. Image fusion may be used to integrate the multidimensional images obtained by polarimetric sensors, multispectral cameras, and various multiplexing techniques. The multidimensional images contain substantially more information compared with two-dimensional (2-D) images or conventional 3-D images. In addition, we present recent progress and applications of 3-D integral imaging including human gesture recognition in the time domain, depth estimation, mid-wave-infrared photon counting, 3-D polarimetric imaging for object shape and material identification, dynamic integral imaging implemented with liquid-crystal devices, and 3-D endoscopy for healthcare applications.B. Javidi wishes to acknowledge support by the National Science Foundation (NSF) under Grant NSF/IIS-1422179, and DARPA and US Army under contract number W911NF-13-1-0485. The work of P. Latorre Carmona, A. Martínez-Uso, J. M. Sotoca and F. Pla was supported by the Spanish Ministry of Economy under the project ESP2013-48458-C4-3-P, and by MICINN under the project MTM2013-48371-C2-2-PDGI, by Generalitat Valenciana under the project PROMETEO-II/2014/062, and by Universitat Jaume I through project P11B2014-09. The work of M. Martínez-Corral and G. Saavedra was supported by the Spanish Ministry of Economy and Competitiveness under the grant DPI2015-66458-C2-1R, and by the Generalitat Valenciana, Spain under the project PROMETEOII/2014/072

Unsupervised Band Selection and Segmentation in Hyper/Multispectral Images

The title of the thesis focuses the attention on hyperspectral image segmentation, that is, we want to detect salient regions in a hyperspectral image and isolate them as accurate as possible. This purpose presents two main problems: Firstly, the fact of using hyperspectral imaging not only give us a huge amount of information, but we also have to face the problem of selecting somehow the information avoiding redundancies.Secondly, the problem of segmentation strictly speaking is still a challenging question whatever the input image would be.This thesis is focused on solving the whole process by means of building an image processing method that analyses and optimises the information acquired by a multispectral device. After that, it detects the main regions that are present in the scene in an image segmentation procedure. Therefore, this work will be divided into two parts. In the first part, an approach for selecting the most relevant subset of input bands will be presented. In the second part, this reduced representation of the initial bands will be the input data of a segmentation method.Finally, the main contributions of this PhD work could be briefly summarised as follows. On the one hand, we have proposed a pre-processing stage with an unsupervised band selection approach based on information measures that reduces considerably the amount of data. This approach has been successfully compared with well-known algorithms of the literature, showing its good performance with regard to pixel image classification tasks. On the other hand, after the band selection stage, two unsupervised segmentation procedures for detecting the main parts in multispectral images have been also developed. Regarding to this segmentation part, we have mainly contributed with two measures of similarity among regions. An objective functional for selecting an optimal (or close to optimal) partition of the image is another relevant contribution too

Modelling contextual constraints in probabilistic relaxation for multi-class semi-supervised learning

This paper proposes a semi-supervised approach based on probabilistic relaxation theory. The algorithm performs a consistent multi-class assignment of labels according to the contextual information constraints. We start from a fully connected graph where each initial sample of the input data is a node of the graph and where only a few nodes have been labelled. A local propagation process is then performed by means of a support function where a new compatibility measure has been proposed. Contributions also include a comparative study of a wide variety of data sets with recent and well-known state-of-the-art algorithms for semi-supervised learning. The results have been provided by an analysis of their statistical significance. Our methodology has demonstrated a noticeably better performance in multi-class classification tasks. Experiments will also show that the proposed technique could be especially useful for applications such as hyperspectral image classification.The authors would like to thank Prof. Pelillo for his help on the proof of convergence in Probabilistic Relaxation approaches and also to Dr. Aykut Erdem for his help with the SSL–GTG algorithm. We deeply thank Dr. Pedro Garcia-Sevilla for his help on the calculation of the algorithms complexity. This work was supported by the Spanish Ministry of Science and Innovation under the Projects Consolider Ingenio 2010 CSD2007-00018, AYA2008-05965-C04-04/ESP and by Caixa-Castelló foundation under the Project P1 1B2007-48

Unsupervised Image Segmentation Using a Hierarchical Clustering Selection Process ⋆

Abstract. In this paper we present an unsupervised algorithm to select the most adequate grouping of regions in an image using a hierarchical clustering scheme. Then, we introduce an optimisation approach for the whole process. The grouping method presented is based on the maximisation of a measure that represents the perceptual decision. The whole strategy takes profit from a hierarchical clustering to find a maximum of the proposed criterion. The algorithm has been used to segment real images as well as multispectral images achieving very accurate results on this task.